OLED device with substituted acridone compounds

ABSTRACT

The invention provides an OLED device comprising a cathode, an anode, and having therebetween a layer containing an acridone compound including a diarylamine or carbazole substituent where the nitrogen of the acridone and the nitrogen of the diarylamine or carbazole are connected by an aromatic hydrocarbon linking group. OLED devices of the invention exhibit improved efficiency and drive voltage.

FIELD OF THE INVENTION

This invention relates to an organic light-emitting diode (OLED)electroluminescent (EL) device that includes acridone compoundssubstituted with diarylamine or carbazole groups.

BACKGROUND OF THE INVENTION

While organic electroluminescent (EL) devices have been known for overtwo decades, their performance limitations have represented a barrier tomany desirable applications. In simplest form, an organic EL device iscomprised of an anode for hole injection, a cathode for electroninjection, and an organic medium sandwiched between these electrodes tosupport charge recombination that yields emission of light. Thesedevices are also commonly referred to as organic light-emitting diodes,or OLEDs. Representative of earlier organic EL devices are Gurnee et al.U.S. Pat. No. 3,172,862, issued Mar. 9, 1965; Gurnee U.S. Pat. No.3,173,050, issued Mar. 9, 1965; Dresner, “Double InjectionElectroluminescence in Anthracene”, RCA Review, 30, 322, (1969); andDresner U.S. Pat. No. 3,710,167, issued Jan. 9, 1973. The organic layersin these devices, usually composed of a polycyclic aromatic hydrocarbon,were very thick (much greater than 1 μm). Consequently, operatingvoltages were very high, often greater than 100V.

More recent organic EL devices include an organic EL element consistingof extremely thin layers (e.g. <1.0 μm) between the anode and thecathode. Herein, the term “organic EL element” encompasses the layersbetween the anode and cathode. Reducing the thickness lowered theresistance of the organic layers and has enabled devices that operate atmuch lower voltage. In a basic two-layer EL device structure, describedfirst in U.S. Pat. No. 4,356,429, one organic layer of the EL elementadjacent to the anode is specifically chosen to transport holes, andtherefore is referred to as the hole-transporting layer, and the otherorganic layer is specifically chosen to transport electrons and isreferred to as the electron-transporting layer. Recombination of theinjected holes and electrons within the organic EL element results inefficient electroluminescence.

There have also been proposed three-layer organic EL devices thatcontain an organic light-emitting layer (LEL) between thehole-transporting layer and electron-transporting layer, such as thatdisclosed by C. Tang et al. (J. Applied Physics, Vol. 65, 3610 (1989)).The light-emitting layer commonly consists of a host material doped witha guest material, otherwise known as a dopant. Still further, there hasbeen proposed in U.S. Pat. No. 4,769,292 a four-layer EL elementcomprising a hole injecting layer (HIL), a hole-transporting layer(HTL), a light-emitting layer (LEL) and anelectron-transporting/injecting layer (ETL). These structures haveresulted in improved device efficiency.

EL devices in recent years have expanded to include not only singlecolor emitting devices, such as red, green and blue, but alsowhite-devices, devices that emit white light. Efficient white lightproducing OLED devices are highly desirable in the industry and areconsidered as a low cost alternative for several applications such aspaper-thin light sources, backlights in LCD displays, automotive domelights, and office lighting. White light producing OLED devices shouldbe bright, efficient, and generally have Commission Internationald'Eclairage (CIE) chromaticity coordinates of about (0.33, 0.33). In anyevent, in accordance with this disclosure, white light is that lightwhich is perceived by a user as having a white color.

Since the early inventions, further improvements in device materialshave resulted in improved performance in attributes such as color,stability, luminance efficiency and manufacturability, e.g., asdisclosed in U.S. Pat. Nos. 5,061,569, 5,409,783, 5,554,450, 5,593,788,5,683,823, 5,908,581, 5,928,802, 6,020,078, and 6,208,077, amongstothers.

Notwithstanding all of these developments, there are continuing needsfor organic EL device components, such as hosts for light-emittinglayers, light-emitting materials, materials for hole transporting layersand/or hole injecting materials, that will provide even lower devicedrive voltages and hence lower power consumption, while maintaining highluminance efficiencies.

The use of acridone materials in OLED devices are known. JP 8-67873 andJP2001-173772 describe the use of N-substituted acridones inlight-emitting layers.

JP2000-056408, JP2005-089544, JP2001-244076 and U.S. Pat. No. 5,811,834all disclose the use of bis-acridones in light-emitting layers.

U.S. Pat. No. 6,894,307 describes the use of acridones as intersystemcrossing agents in light emitting layers.

CN1660844 discloses quinacridones linked to a carbazole group withsaturated alkyl chains. JP2005093098 and JP2007191439 disclosequinacridones linked to carbazole groups but not through the nitrogen ofthe quinacridone.

However, these devices do not have all desired EL characteristics interms of high efficiency and low drive voltages.

Notwithstanding all these developments, there remains a need to increaseefficiency and lower drive voltage of OLED devices, as well as toprovide embodiments with other improved features.

SUMMARY OF THE INVENTION

The invention provides an OLED device comprising a cathode, an anode,and having therebetween a layer containing an acridone compoundincluding a diarylamine or carbazole substituent where the nitrogen ofthe acridone and the nitrogen of the diarylamine or carbazole areconnected by an aromatic hydrocarbon linking group. OLED devices of theinvention exhibit improved efficiency and drive voltage.

The invention also provides an improved process and display employingthe device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-sectional view of one embodiment of theOLED device of the present invention. It will be understood that FIG. 1is not to scale since the individual layers are too thin and thethickness differences of various layers are too great to permitdepiction to scale.

DETAILED DESCRIPTION OF THE INVENTION

The invention is generally as described above. An OLED device of theinvention is a multilayer electroluminescent device comprising acathode, an anode, light-emitting layer(s) (LEL), electron-transportinglayer(s) (ETL) and electron-injecting layer(s) (EIL) and optionallyadditional layers such as hole-injecting layer(s) (HIL),hole-transporting layer(s) (HTL), exciton-blocking layer(s) (XBL),spacer layer(s), connecting layer(s) and hole-blocking layer(s) (HBL).

The acridone material of the invention has excellent hole-transportingproperties. It can be used in any of the typical OLED applicationsrequiring hole-transporting materials. For example, it may be used inhole-injecting layers, hole transporting layers, light-emitting layersand exciton-blocking layers. The most preferred use is as a non-emittinghost material in combination with a light-emitting dopant material in alight-emitting layer.

A host material is preferably chosen to efficiently produce exciteddopant molecules. In addition, the host and dopant combination should bechosen such that not only is the energy transfer from the host to thedopant efficient, and also that the probability of reverse energytransfer from the dopant to the host is low. It is usually desirable forsubstantially all of the luminescence to have the spectrum of thedopant, rather than the host. By ‘substantially all’, it is meant thatmore than about 90% of the emitted photons come from the dopant(s). Thedegree to which the host and the dopant contribute to the emission canbe determined by comparing the emission spectrum of the device with theemission spectra of the individual components.

To achieve the proper energy-transfer properties, the host and thedopant are typically selected such that the energy of the excited stateof the dopant is lower than that of the host, that the host have someemission in the absence of the dopant, and that the emission of the hostoverlaps with the absorption of the dopant. The efficiency of emissionby the host however, may be inferior to that by the dopant. In thisusage, the acridone host material should not emit substantial amounts oflight when a potential is applied to the OLED. By substantial, it ismeant that the host material emits no more than about 10%, andpreferably no more than 2%, of the total light from that layer. Theconcentration of the dopant may be adjusted to optimize the energytransfer and the efficiency with which the dopant luminesces. Ingeneral, the optimum dopant concentration is small compared to that ofthe host. Too low a dopant concentration generally results in undesiredemission from the host, and frequently low efficiency. Too high a dopantconcentration typically results in reduced efficiency and undesiredspectral shifts, phenomena described as concentration quenching orself-quenching. Suitably, host concentrations in the light-emittinglayer should be 50% or greater; more suitably, 75% or greater; or mostsuitably, 88% or greater with the dopant concentration to becorrespondingly, 50% or less; 25% or less, most typically in the rangeof 0.5 to 15% with the most desirable range being from 1% to 12%. Theremay be one or more other host materials additionally present in the LEL.Any material known to be a suitable host for a light-emitting layer canbe used as a co-host. It may have hole-transporting properties,electron-transporting properties or possess the ability to do both.Whenever the acridone of the invention is used as a host together withanother co-host material, it is preferred that the acridone materialcomprises at least 2% of the total amount of materials in the LEL, ormore preferably, at least 10%.

Further descriptions of the requirements for host and dopant materialscan be found in Chen et al, Macromolecular Symposia (1997), 125, 1-48and U.S. Pat. No. 7,221,088.

The light-emitting materials used with the acridone host may befluorescent or phosphorescent. While the light-emitting compound ispresent in the LEL at 50% or less; 25% or less, most typically in therange of 0.5 to 15% with the most desirable range being from 1% to 12%.There may be more than one light-emitting material that emits the sameor different colors of light in the LEL. The acridones of the inventionare particularly well suited for use with phosphorescent dopants.

In another embodiment, the acridone compound can be a light-emittingdopant and be used as the only material in the LEL or in combinationwith one or more non-light emitting host compounds. One example of asuitable acridone for this usage would be a derivative of a quinacridonesuch as example A-12.

The acridones of the invention are N-substituted derivatives of9(10H)-acridanone:

where the R substituent on the nitrogen comprises of an aromatichydrocarbon linking group bearing a diarylamine or carbazole group. Thephenyl rings of the acridone may be substituted including annulated orfused rings. An example of a substituted acridone would be anquinacridone. However, it is preferred that the phenyl rings of theacridone molecule are unsubstituted.

The aromatic hydrocarbon linking group is preferably composed of aunbroken chain of 6 to 36 carbon atoms that connect the nitrogen of theacridone to the nitrogen of the diarylamine or carbazole group. Thereare 3 general types of useful linking groups. One type of linking groupis an aromatic hydrocarbon composed solely of one fused aromatic ringsystem connected to the nitrogens by single bonds. Examples of this typewould be a phenyl ring, a naphthalene or an anthracene. Another type oflinking group is composed of a series of aromatic rings each connecteddirectly by single bonds. An example of this would be a para-biphenyllinking group. A third type of linking group would contain ethylene oracetylene groups which may also contain aromatic rings, either as asubstituent or as part of the chain. Thus, it should be understood thatthe term ‘aromatic hydrocarbon linking group’ also includes olefinic(—CH═CH—) or acetylenic (—C≡C) groups as well as rings when referring tothe unbroken chain of the linking group of the invention. In every case,all of the carbons in the unbroken chain of the linking group should besp or sp² hybridized. Although the preferred linking group is a chain ofaromatic, olefinic or acetylenic carbon atoms containing only hydrogenas substituents, it may have further substituents including heteroatomspendant on the carbon chain. The most preferred linking groups arearomatic rings including phenyl, biphenyl (o, m, p-linked), fluorenyl,naphthyl, anthracenyl, fluoranthenyl and phenanthrenyl.

In one type of compound of the invention, the linking group is attachedto the nitrogen of a diarylamine group. The aryl groups on the nitrogenare each composed of an aromatic group of 6 to 30 carbon atoms and maybe the same or different. The aryl groups may be further substituted.Preferred examples of the aryl group are phenyl and naphthyl. However,the aryl groups in the diarylamine group cannot be connected together bya ketone group to form an acridone moiety.

In another type of compound of the invention, the linking group isattached to the nitrogen of a carbazole group. A carbazole group is ananalog of a diphenylamine where the phenyl rings are directly linkedtogether and has the following general structure:

where the linking group R as described above is attached to the nitrogenof the carbazole group. The carbazole group may be further substitutedand may have fused or annulated rings.

Preferred acridone compound are according to Formula (I):

wherein:

R₁ and R₂ are substituents;

x and y are independently 0 to 4;

L is a linking group consisting of an unbroken chain of 6 to 36aromatic, olefinic or acetylenic carbon atoms; and

Ar₁ and Ar₂ are independently aromatic groups of 6 to 30 carbon atoms orare connected together to form a carbazole group.

The optional substituents R₁ and R₂ on the acridone nucleus can be anysubstituent. Examples of suitable substituents include alkyl groups,aryl groups, heterocyclic groups and may represent fused or annulatedrings. R₁ and R₂ can be the same or different. One specific example iswhere R₁ and R₂ together form a fused acridone ring to form anquinacridone. Preferred compounds are where both x and y are 0.

In the linking group, the chain may be composed of 6 to 36 aromatic,olefinic or acetylenic carbon atoms attached together in anycombination. There may not be any heteroatoms between these carbon atomsin the chain. Preferred L groups are composed only of aromatic carbonatoms including phenyl, p-biphenyl or naphtbyl.

Preferred Ar₁ and Ar₂ are where both are substituted or unsubstitutedphenyl, one is phenyl and the other naphthyl, or together both form asubstituted or unsubstituted carbazole ring. Most preferred is where Ar₁and Ar₂ are both phenyl or together form an unsubstituted carbazolering.

Specific examples of acridone materials of the invention are as follows:

A light-emitting layer containing the acridone derivative can emit inany color or combination of colors of light. When referring to the colorof light emitter, it should be understood that lesser amounts ofdifferent color of light may be emitted as well. For example, bluelight-emission would refer to a layer where blue light predominates butmay emit smaller amounts of green or red as well. The OLED devicecontaining the invention may be a single color or may emit white light.

FIG. 1 shows one embodiment of the invention in which light-emittinglayers, electron-transporting and electron-injecting layers are present.The acridone compounds of the invention can be located in thelight-emitting layer (LEL, 134), the hole-injection layer (HIL, 130) orthe hole-transporting layer (HTL, 132) among others. An optionalhole-blocking layer (HBL, 135) is shown between the light-emitting layerand the electron-transporting layer. The figure also shows an optionalhole-injecting layer (HIL, 130). In another embodiment, there is nohole-blocking layer (HBL, 135) located between the ETL and the LEL. Inyet other embodiments, there may be more than one hole-injecting,electron-injecting and electron-transporting layers.

In one suitable embodiment the EL device includes a means for emittingwhite light, which may include complimentary emitters or a white emitterwith filtering means. The device may also include combinations offluorescent emitting materials and phosphorescent emitting materials(sometimes referred to as hybrid OLED devices). To produce a whiteemitting device, ideally the hybrid fluorescent/phosphorescent devicewould comprise a blue fluorescent emitter and proper proportions of agreen and red phosphorescent emitter, or other color combinationssuitable to make white emission. However, hybrid devices havingnon-white emission may also be useful by themselves. Hybridfluorescent/phosphorescent elements having non-white emission may alsobe combined with additional phosphorescent elements in series in astacked OLED. For example, white emission may be produced by one or morehybrid blue fluorescent/red phosphorescent elements stacked in serieswith a green phosphorescent element using p/n junction connectors asdisclosed in Tang et al U.S. Pat. No. 6,936,961B2. This invention may beused in so-called stacked device architecture, for example, as taught inU.S. Pat. Nos. 5,703,436 and 6,337,492.

In one desirable embodiment the EL device is part of a display device.In another suitable embodiment the EL device is part of an area lightingdevice.

The EL device of the invention is useful in any device where stablelight emission is desired such as a lamp or a component in a static ormotion imaging device, such as a television, cell phone, DVD player, orcomputer monitor.

As used herein and throughout this application, the term carbocyclic andheterocyclic rings or groups are generally as defined by the Grant &Hackh's Chemical Dictionary, Fifth Edition, McGraw-Hill Book Company. Acarbocyclic ring is any aromatic or non-aromatic ring system containingonly carbon atoms and a heterocyclic ring is any aromatic ornon-aromatic ring system containing both carbon and non-carbon atomssuch as nitrogen (N), oxygen (O), sulfur (S), phosphorous (P), silicon(Si), gallium (Ga), boron (B), beryllium (Be), indium (In), aluminum(Al), and other elements found in the periodic table useful in formingring systems. For the purpose of this invention, also included in thedefinition of a heterocyclic ring are those rings that includecoordinate bonds. The definition of a coordinate or dative bond can befound in Grant & Hackh's Chemical Dictionary, pages 91 and 153. Inessence, a coordinate bond is formed when electron rich atoms such as Oor N, donate a pair of electrons to electron deficient atoms or ionssuch as aluminum, boron or alkali metal ions such as Li⁺, Na⁺, K⁺ andCs⁺. One such example is found in tris(8-quinolinolato)aluminum(III),also referred to as Alq, wherein the nitrogen on the quinoline moietydonates its lone pair of electrons to the aluminum atom thus forming theheterocycle and hence providing Alq with a total of 3 fused rings. Thedefinition of a ligand, including a multidentate ligand, can be found inGrant & Hackh's Chemical Dictionary, pages 337 and 176, respectively.

Unless otherwise specifically stated, use of the term “substituted” or“substituent” means any group or atom other than hydrogen. Additionally,when the term “group” is used, it means that when a substituent groupcontains a substitutable hydrogen, it is also intended to encompass notonly the substituent's unsubstituted form, but also its form furthersubstituted with any substituent group or groups as herein mentioned, solong as the substituent does not destroy properties necessary for deviceutility. Suitably, a substituent group may be halogen or may be bondedto the remainder of the molecule by an atom of carbon, silicon, oxygen,nitrogen, phosphorous, sulfur, selenium, or boron. The substituent maybe, for example, halogen, such as chloro, bromo or fluoro; nitro;hydroxyl; cyano; carboxyl; or groups which may be further substituted,such as alkyl, including straight or branched chain or cyclic alkyl,such as methyl, trifluoromethyl, ethyl, t-butyl,3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such asethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy,2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy,2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such asphenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, suchas phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy;carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido,alpha-(2,4-di-t-pentyl-phenoxy)acetamido,alpha-(2,4-di-t-pentylphenoxy)butyramido,alpha-(3-pentadecylphenoxy)-hexanamido,alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido,2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl,N-methyltetradecanamido, N-succinimido, N-phthalimido,2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, andN-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino,benzyloxycarbonylamino, hexadecyloxycarbonylamino,2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino,2,5-(di-t-pentylphenyl)carbonylamino, p-dodecyl-phenylcarbonylamino,p-tolylcarbonylamino, N-methylureido, N′N-dimethylureido,N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido,N,N-dioctyl-N′-ethylureido, N-phenylureido, N,N-diphenylureido,N-phenyl-N-p-tolylureido, N-(m-hexadecylphenyl)ureido,N,N-(2,5-di-t-pentylphenyl)-N′-ethylureido, and t-butylcarbonamido;sulfonamido, such as methyl sulfonamido, benzenesulfonamido,p-tolylsulfonamido, p-dodecylbenzenesulfonamido,N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, andhexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl,N-ethylsulfamoyl, N N-dipropylsulfamoyl, N-hexadecylsulfamoyl,NN-dimethylsulfamoyl, N-[3-(dodecyloxy)propyl]sulfamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl,N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, suchas N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl,N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such asacetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl,p-dodecyloxyphenoxycarbonyl methoxycarbonyl, butoxycarbonyl,tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl,3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such asmethoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl,2-ethylhexyloxysulfonyl, phenoxysulfonyl,2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl,2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl,phenylsulfonyl, 4-nonylphenylsulfonyl, and p-tolylsulfonyl; sulfonyloxy,such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such asmethylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl,hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, andp-tolylsulfinyl; thio, such as ethylthio, octylthio, benzylthio,tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio,2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such asacetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy,N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy;amine, such as phenylanilino, 2-chloroanilino, diethylamine,dodecylamine; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or3-benzylhydantoinyl; phosphate, such as dimethylphosphate andethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; aheterocyclic group, a heterocyclic oxy group or a heterocyclic thiogroup, each of which may be substituted and which contain a 3 to 7membered heterocyclic ring composed of carbon atoms and at least onehereto atom selected from the group consisting of oxygen, nitrogen,sulfur, phosphorous, or boron. Such as 2-furyl, 2-thienyl,2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such astriethylammonium; quaternary phosphonium, such as triphenylphosphonium;and silyloxy, such as trimethylsilyloxy.

If desired, the substituents may themselves be further substituted oneor more times with the described substituent groups. The particularsubstituents used may be selected by those skilled in the art to attaindesirable properties for a specific application and can include, forexample, electron-withdrawing groups, electron-donating groups, andsteric groups. When a molecule may have two or more substituents, thesubstituents may be joined together to form a ring such as a fused ringunless otherwise provided. Generally, the above groups and substituentsthereof may include those having up to 48 carbon atoms, typically 1 to36 carbon atoms and usually less than 24 carbon atoms, but greaternumbers are possible depending on the particular substituents selected.

The following is the description of the layer structure, materialselection, and fabrication process for OLED devices.

General OLED Device Architecture

The present invention can be employed in many OLED configurations usingsmall molecule materials, oligomeric materials, polymeric materials, orcombinations thereof. These include from very simple structures having asingle anode and cathode to more complex devices, such as passive matrixdisplays having orthogonal arrays of anodes and cathodes to form pixels,and active-matrix displays where each pixel is controlled independently,for example, with thin film transistors (TFTs). There are numerousconfigurations of the organic layers wherein the present invention issuccessfully practiced. For this invention, essential requirements are acathode, an anode, a LEL, an ETL and a HIL.

One embodiment according to the present invention and especially usefulfor a small molecule device is shown in FIG. 1. OLED 100 contains asubstrate 110, an anode 120, a hole-injecting layer 130, ahole-transporting layer 132, a light-emitting layer 134, a hole-blockinglayer 135, an electron-transporting layer 136, an electron-injectinglayer 138 and a cathode 140. In some other embodiments, there areoptional spacer layers on either side of the LEL. These spacer layers donot typically contain light emissive materials. All of these layer typeswill be described in detail below. Note that the substrate mayalternatively be located adjacent to the cathode, or the substrate mayactually constitute the anode or cathode. Also, the total combinedthickness of the organic layers is preferably less than 500 nm.

The anode and cathode of the OLED are connected to a voltage/currentsource 150, through electrical conductors 160. Applying a potentialbetween the anode and cathode such that the anode is at a more positivepotential than the cathode operates the OLED. Holes are injected intothe organic EL element from the anode. Enhanced device stability cansometimes be achieved when the OLED is operated in an AC mode where, forsome time period in cycle, the potential bias is reversed and no currentflows. An example of an AC driven OLED is described in U.S. Pat. No.5,552,678.

Anode

When the desired EL emission is viewed through the anode, anode 120should be transparent or substantially transparent to the emission ofinterest. Common transparent anode materials used in this invention areindium-tin oxide (ITO), indium-zinc oxide (IZO) and tin oxide, but othermetal oxides can work including, but not limited to, aluminum- orindium-doped zinc oxide, magnesium-indium oxide, and nickel-tungstenoxide. In addition to these oxides, metal nitrides, such as galliumnitride, and metal selenides, such as zinc selenide, and metal sulfides,such as zinc sulfide, can be used as the anode 120. For applicationswhere EL emission is viewed only through the cathode 140, thetransmissive characteristics of the anode 120 are immaterial and anyconductive material can be used, transparent, opaque or reflective.Example conductors for this application include, but are not limited to,gold, iridium, molybdenum, palladium, and platinum. Typical anodematerials, transmissive or otherwise, have a work function of 4.1 eV orgreater. Desired anode materials are commonly deposited by any suitablemeans such as evaporation, sputtering, chemical vapor deposition, orelectrochemical means. Anodes can be patterned using well-knownphotolithographic processes. Optionally, anodes may be polished prior toapplication of other layers to reduce surface roughness so as tominimize short circuits or enhance reflectivity.

Hole Injection Layer

Although it is not always necessary, it is often useful to provide anHIL in the OLEDs. HIL 130 in the OLEDs can serve to facilitate holeinjection from the anode into the HTL, thereby reducing the drivevoltage of the OLEDs. Suitable materials for use in HIL 130 include, butare not limited to, porphyrinic compounds as described in U.S. Pat. No.4,720,432 and some aromatic amines, for example,4,4′,4″-tris[(3-ethylphenyl)phenylamino]triphenylamine (m-TDATA).Alternative hole-injecting materials reportedly useful in OLEDs aredescribed in EP 0 891 121 A1 and EP 1 029 909 A1. Aromatic tertiaryamines discussed below can also be useful as hole-injecting materials.Other useful hole-injecting materials such asdipyrazino[2,3-f:2′,3′-h]quinoxalinehexacarbonitrile are described inU.S. Patent Application Publication 2004/0113547 A1 and U.S. Pat. No.6,720,573. In addition, a p-type doped organic layer is also useful forthe HIL as described in U.S. Pat. No. 6,423,429. The term “p-type dopedorganic layer” means that this layer has semiconducting properties afterdoping, and the electrical current through this layer is substantiallycarried by the holes. The conductivity is provided by the formation of acharge-transfer complex as a result of hole transfer from the dopant tothe host material.

The thickness of the HIL 130 is in the range of from 0.1 nm to 200 nm,preferably, in the range of from 0.5 nm to 150 nm.

Hole Transport Layer

The HTL 132 contains at least one hole-transporting material such as anaromatic tertiary amine, where the latter is understood to be a compoundcontaining at least one trivalent nitrogen atom that is bonded only tocarbon atoms, at least one of which is a member of an aromatic ring. Inone form the aromatic tertiary amine is an arylamine, such as amonoarylamine, diarylamine, triaylamine, or a polymeric arylamine.Exemplary monomeric triarylamines are illustrated by Klupfel et al. U.S.Pat. No. 3,180,730. Other suitable triarylamines substituted with one ormore vinyl radicals or at least one active hydrogen-containing group aredisclosed by Brantley, et al. in U.S. Pat. Nos. 3,567,450 and 3,658,520.

A more preferred class of aromatic tertiary amines are those whichinclude at least two aromatic tertiary amine moieties as described inU.S. Pat. Nos. 4,720,432 and 5,061,569. Such compounds include thoserepresented by structural Formula (A)

wherein:

-   -   Q₁ and Q₂ are independently selected aromatic tertiary amine        moieties; and    -   G is a linking group such as an arylene, cycloalkylene, or        alkylene group of a carbon to carbon bond.

In one embodiment, at least one of Q₁ or Q₂ contains a polycyclic fusedring structure, e.g., a naphthalene. When G is an aryl group, it isconveniently a phenylene, biphenylene, or naphthalene moiety.

A useful class of triarylamines satisfying structural Formula A andcontaining two triarylamine moieties is represented by structuralFormula (B)

wherein:

-   -   R₁ and R₂ each independently represents a hydrogen atom, an aryl        group, or an alkyl group or R₁ and R₂ together represent the        atoms completing a cycloalkyl group; and    -   R₃ and R₄ each independently represents an aryl group, which is        in turn substituted with a diaryl substituted amino group, as        indicated by structural Formula (C)

wherein:

-   -   R₅ and R₆ are independently selected aryl groups. In one        embodiment, at least one of R₅ or R₆ contains a polycyclic fused        ring structure, e.g., a naphthalene.

Another class of aromatic tertiary amines are the tetraaryldiamines.Desirable tetraaryldiamines include two diarylamino groups, such asindicated by Formula (C), linked through an arylene group. Usefultetraaryldiamines include those represented by Formula (D)

wherein:

-   -   each ARE is an independently selected arylene group, such as a        phenylene or anthracene moiety;    -   n is an integer of from 1 to 4; and    -   Ar, R₇, R₈, and R₉ are independently selected aryl groups. In a        typical embodiment, at least one of Ar, R₇, R₈, and R₉ is a        polycyclic fused ring structure, e.g., a naphthalene.

Another class of the hole-transporting material comprises a material offormula (E);

In formula (E), Ar₁—Ar₆ independently represent aromatic groups, forexample, phenyl groups or tolyl groups;

R₁-R₁₂ independently represent hydrogen or independently selectedsubstituent, for example an alkyl group containing from 1 to 4 carbonatoms, an aryl group, a substituted aryl group.

The various alkyl, alkylene, aryl, and arylene moieties of the foregoingstructural Formulae (A), (B), (C), (D), and (E) can each in turn besubstituted. Typical substituents include alkyl groups, alkoxy groups,aryl groups, aryloxy groups, and halogen such as fluoride, chloride, andbromide. The various alkyl and alkylene moieties typically contain fromabout 1 to 6 carbon atoms. The cycloalkyl moieties can contain from 3 toabout 10 carbon atoms, but typically contain five, six, or seven ringcarbon atoms, e.g. cyclopentyl, cyclohexyl, and cycloheptyl ringstructures. The aryl and arylene moieties are typically phenyl andphenylene moieties.

The HTL is formed of a single or a mixture of aromatic tertiary aminecompounds. Specifically, one can employ a triarylamine, such as atriarylamine satisfying the Formula (B), in combination with atetraaryldiamine, such as indicated by Formula (D). When a triarylamineis employed in combination with a tetraaryldiamine, the latter ispositioned as a layer interposed between the triarylamine and theelectron injecting and transporting layer. Aromatic tertiary amines areuseful as hole-injecting materials also. Illustrative of useful aromatictertiary amines are the following:

-   -   1,1-bis(4-di-p-tolylaminophenyl)cyclohexane;    -   1,1-bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane;    -   1,5-bis[N-(1-naphthyl)-N-phenylamino]naphthalene;    -   2,6-bis(di-p-tolylamino)naphthalene;    -   2,6-bis[di-(1-naphthyl)amino]naphthalene;    -   2,6-bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene;    -   2,6-bis[N,N-di(2-naphthyl)amine]fluorene;    -   4-(di-p-tolylamino)-4′-[4(di-p-tolylamino)-styryl]stilbene;    -   4,4′-bis(diphenylamino)quadriphenyl;    -   4,4″-bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl;    -   4,4′-bis[N-(1-coronenyl)-N-phenylamino]biphenyl;    -   4,4′-bis[N-(1-naphthyl)-N-phenylanino]biphenyl (NPB);    -   4,4′-bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB);    -   4,4″-bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl;    -   4,4′-bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl;    -   4,4′-bis[N-(2-naphthyl)-N-phenylamino]biphenyl;    -   4,4′-bis[N-(2-perylenyl)-N-phenylamino]biphenyl;    -   4,4′-bis[N-(2-phenanthryl)-N-phenylamino]biphenyl;    -   4,4′-bis[N-(2-pyrenyl)-N-phenylamino]biphenyl;    -   4,4′-bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl;    -   4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD);    -   4,4′-bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl;    -   4,4′-bis[N-(9-anthryl)-N-phenylamino]biphenyl;    -   4,4′-bis{N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl;    -   4,4′-bis[N-phenyl-N-(2-pyrenyl)amino]biphenyl;    -   4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine        (m-TDATA);    -   Bis(4-dimethylamino-2-methylphenyl)-phenylmethane,    -   N-phenylcarbazole;    -   N,N′-bis[4-([1,1′-biphenyl]-4-ylphenylamino)phenyl]-N,N′-di-1-naphthalenyl-[1,1-biphenyl]-4,4′-diamine;    -   N,N′-bis[4-(di-1-naphthalenylamino)phenyl]-N,N′-di-1-naphthalenyl-[1,1′-biphenyl]-4,4′-diamine;    -   N,N′-bis[4-[(3-methylphenyl)phenylamino]phenyl]-N,N′-dipbenzyl-[[1,1]biphenyl]-4,4′-diamine;    -   N,N-bis[4-(diphenylamino)phenyl]-N′,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine;    -   N,N′-di-1-naphthalenyl-N,N′-bis[4-(1-naphthalenylphenylamino)phenyl]-[1,1′-biphenyl]-4,4′-diamine;    -   N,N′-di-1-naphthalenyl-N,N′-bis[4-(2-naphthalenylphenylamino)phenyl]-[1,1′-biphenyl]-4,4′-diamine;    -   N,N,N-tri(p-tolyl)amine;    -   N,N,N′,N′-tetra-p-tolyl-4-4′-diaminobiphenyl;    -   N,N,N′,N′-tetraphenyl-4,4′-diaminobiphenyl;    -   N,N,N′,N′-tetra-1-naphthyl-4,4′-diaminobiphenyl;    -   N,N,N′,N′-tetra-2-naphthyl-4,4′-diaminobiphenyl; and    -   N,N,N′,N′-tetra(2-naphthyl)-4,4″-diamino-p-terphenyl.

Another class of useful hole-transporting materials includes polycyclicaromatic compounds as described in EP 1 009 041. Tertiary aromaticamines with more than two amine groups can be used including oligomericmaterials. In addition, polymeric hole-transporting materials are usedsuch as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole,polyaniline, and copolymers such aspoly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) also calledPEDOT/PSS.

The thickness of the HTL 132 is in the range of from 5 nm to 200 n m,preferably, in the range of from 10 nm to 150 mu.

Exciton Blocking Layer (EBL)

An optional exciton- or electron-blocking layer may be present betweenthe HTL and the LEL (not shown in FIG. 1). Some suitable examples ofsuch blocking layers are described in U.S. App 20060134460 A1.

Light Emitting Layer

As more fully described in U.S. Pat. Nos. 4,769,292 and 5,935,721, thelight-emitting layer(s) (LEL) 134 of the organic EL element shown inFIG. 1 comprises a luminescent, fluorescent or phosphorescent materialwhere electroluminescence is produced as a result of electron-hole pairrecombination in this region. The light-emitting layer can be comprisedof a single material, but more commonly consists ofnon-electroluminescent compounds (generally referred to as the host)doped with an electroluminescent or light-emitting guest compound(generally referred to as the dopant) or compounds where light emissioncomes primarily from the electroluminescent compound and can be of anycolor. In one aspect of this invention, the host is an acridonederivative. The non-electroluminescent compounds can be coated as 0.01to less than 50% by volume into the non-electroluminescent componentmaterial, but typically coated as 0.01 to 25% and more typically coatedas 0.05 to 15% into the non-electroluminescent component. In thisinvention, the most desirable range for the light-emitting compound is 1to 12%. The thickness of the LEL can be any suitable thickness. It canbe in the range of from 0.1 mm to 100 mm.

A LEL can be a single light-emitting layer or a light-emitting zonecomposed of a series of individual light-emitting sublayers. Thesesublayers can emit the same or different colors of light.

An important relationship for choosing a dye as a electroluminescentcomponent is a comparison of the band gap potential which is defined asthe energy difference between the highest occupied molecular orbital andthe lowest unoccupied molecular orbital of the molecule. For efficientenergy transfer from the non-electroluminescent compound to theelectroluminescent compound molecule, a necessary condition is that theband gap of the electroluminescent compound is smaller than that of thenon-electroluminescent compound or compounds. Thus, the selection of anappropriate host material is based on its electronic characteristicsrelative to the electronic characteristics of the electroluminescentcompound, which itself is chosen for the nature and efficiency of thelight emitted. As described below, fluorescent and phosphorescentdopants typically have different electronic characteristics so that themost appropriate hosts for each may be different. However in some cases,the same host material can be useful for either type of dopant.

Non-electroluminescent compounds and emitting molecules known to be ofuse include, but are not limited to, those disclosed in U.S. Pat. Nos.4,768,292, 5,141,671, 5,150,006, 5,151,629, 5,405,709, 5,484,922,5,593,788, 5,645,948, 5,683,823, 5,755,999, 5,928,802, 5,935,720,5,935,721, and 6,020,078.

a) Phosphorescent Light Emitting Layers

Suitable hosts for phosphorescent LELs should be selected so thattransfer of a triplet exciton can occur efficiently from the host to thephosphorescent dopant(s) but cannot occur efficiently from thephosphorescent dopant(s) to the host. Therefore, it is highly desirablethat the triplet energy of the host be higher than the triplet energiesof phosphorescent dopant. Generally speaking, a large triplet energyimplies a large optical band gap. However, the band gap of the hostshould not be chosen so large as to cause an unacceptable barrier toinjection of holes into the fluorescent LEL and an unacceptable increasein the drive voltage of the OLED. The host in a phosphorescent LEL mayinclude any of the aforementioned hole-transporting material used forthe HTL 132, as long as it has a triplet energy higher than that of thephosphorescent dopant in the layer. The host used in a phosphorescentLEL can be the same as or different from the hole-transporting materialused in the HTL 132. In some cases, the host in the phosphorescent LELmay also suitably include an electron-transporting material (it will bediscussed thereafter), as long as it has a triplet energy higher thanthat of the phosphorescent dopant.

In addition to the aforementioned hole-transporting materials in the HTL132, there are several other classes of hole-transporting materialssuitable for use as the host in a phosphorescent LEL.

One desirable host comprises a hole-transporting material of formula(F):

In formula (F), R₁ and R₂ represent substituents, provided that R₁ andR₂ can join to form a ring. For example, R₁ and R₂ can be methyl groupsor join to form a cyclohexyl ring;

Ar₁—Ar₄ represent independently selected aromatic groups, for examplephenyl groups or tolyl groups;

R₃-R₁₀ independently represent hydrogen, alkyl, substituted alkyl, aryl,substituted aryl group.

Examples of suitable materials include, but are not limited to:

-   -   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)cyclohexane (TAPC);    -   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)cyclopentane;    -   4,4′-(9H-fluoren-9-ylidene)bis[N,N-bis(4-methylphenyl)-benzenamine;    -   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)-4-phenylcyclohexane;    -   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)-4-methylcyclohexane;    -   1,1-Bis(4-(N,N-di-p-tolylamino)phenyl)-3-phenylpropane;    -   Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylpenyl)methane;    -   Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)ethane;    -   4-(4-Diethylaminophenyl)triphenylmethane;    -   4,4′-Bis(4-diethylaminophenyl)diphenylmethane.

A useful class of triarylamines suitable for use as the host includescarbazole derivatives such as those represented by formula (G);

-   -   In formula (G), Q independently represents nitrogen, carbon, an        aryl group, or substituted aryl group, preferably a phenyl        group;    -   R₁ is preferably an aryl or substituted aryl group, and more        preferably a phenyl group, substituted phenyl, biphenyl,        substituted biphenyl group;    -   R₂ through R₇ are independently hydrogen, alkyl, phenyl or        substituted phenyl group, aryl amine, carbazole, or substituted        carbazole;    -   and n is selected from 1 to 4.

Another useful class of carbazoles satisfying structural formula (G) isrepresented by formula (H):

wherein:

-   -   n is an integer from 1 to 4;    -   Q is nitrogen, carbon, an aryl, or substituted aryl;    -   R₂ through R₇ are independently hydrogen, an alkyl group, phenyl        or substituted phenyl, an aryl amine, a carbazole and        substituted carbazole.

Illustrative of useful substituted carbazoles are the following:

-   -   4-(9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]-benzenamine        (TCTA);    -   4-(3-phenyl-9H-carbazol-9-yl)-N,N-bis[4(3-phenyl-9H-carbazol-9-yl)phenyl]-benzenamine;    -   9,9′-[5′-[4-(9H-carbazol-9-yl)phenyl][1,1:3′,        1″-terphenyl]-4,4′-diyl]bis-9H-carbazole.    -   9,9′-(2,2′-dimethyl[1,1-biphenyl]-4,4′-diyl)bis-9H-carbazole        (CDBP);    -   9,9′-[1,1′-biphenyl]-4,4′-diylbis-9H-carbazole (CBP);    -   9,9′-(1,3-phenylene)bis-9H-carbazole (mCP);    -   9,9′-(1,4-phenylene)bis-9H-carbazole;    -   9,9′,9″-(1,3,5-benzenetriyl)tris-9H-carbazole;    -   9,9′-(1,4-phenylene)bis[N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine;    -   9-[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenyl-9H-carbazol-3-amine;    -   9,9′-(1,4-phenylene)bis[N,N-diphenyl-9H-carbazol-3-amine;    -   9-[4-(9H-carbazol-9-yl)phenyl]-N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine.

The above classes of hosts suitable for phosphorescent LELs may also beused as hosts in fluorescent LELs as well.

Suitable phosphorescent dopants for use in a phosphorescent LEL can beselected from the phosphorescent materials described by formula (J)below:

wherein:

-   -   A is a substituted or unsubstituted heterocyclic ring containing        at least one nitrogen atom;    -   B is a substituted or unsubstituted aromatic or heteroaromatic        ring, or ring containing a vinyl carbon bonded to M;    -   X—Y is an anionic bidentate ligand;    -   m is an integer from 1 to 3 and    -   n in an integer from 0 to 2 such that m+n=3 for M=Rh or Ir; or    -   m is an integer from 1 to 2 and n in an integer from 0 to 1 such        that m+n=2 for M=Pt or Pd.

Compounds according to formula (J) may be referted to as C,N—(or C´N—)cyclometallated complexes to indicate that the central metal atom iscontained in a cyclic unit formed by bonding the metal atom to carbonand nitrogen atoms of one or more ligands. Examples of heterocyclic ringA in formula (J) include substituted or unsubstituted pyridine,quinoline, isoquinoline, pyrimidine, indole, indazole, thiazole, andoxazole rings. Examples of ring B in formula (J) include substituted orunsubstituted phenyl, naphthyl, thienyl, benzothienyl, furanyl rings.Ring B in formula (J) may also be a N-containing ring such as pyridine,with the proviso that the N-containing ring bonds to M through a C atomas shown in formula (J) and not the N atom.

An example of a tris-C,N-cyclometallated complex according to formula(J) with m=3 and n=0 is tris(2-phenyl-pyridinato-N,C^(2′)-)Iridium(III), shown below in stereodiagrams as facial (fac-) or meridional(mer-) isomers.

Generally, facial isomers are preferred since they are often found tohave higher phosphorescent quantum yields than the meridional isomers.

-   -   Additional examples of tris-C,N-cyclometallated phosphorescent        materials according to formula (J) are        tris(2-(4′-methylphenyl)pyridinato-N,C^(2′))Iridium(III),        tris(3-phenylisoquinolinato-N,C^(2′))Iridium(III),        tris(2-phenylquinolinato-N,C^(2′))Iridium(III),        tris(1-phenylisoquinolinato-N,C^(2′))Iridium(III),        tris(1-(4′-methylphenyl)isoquinolinato-N,C^(2′))Iridium(III),        tris(2-(4′,6′-difluorophenyl)-pyridinato-N,C^(2′))Iridium(III),        tris(2-((5′-phenyl)-phenyl)pyridinato-N,C^(2′))Iridium(III),        tris(2-(2′-benzothienyl)pyridinato-N,C^(3′))Iridium(III),        tris(2-phenyl-3,3′dimethyl)indolato-N,C^(2′))Ir(III),        tris(1-phenyl-1H-indazolato-N,C^(2′))Ir(III).

Of these, tris(1-phenylisoquinoline) iridium (III) (also referred to asIr(piq)₃) and tris(2-phenylpyridine) iridium (also referred to asIr(ppy)₃) are particularly suitable for this invention.

Tris-C,N-cyclometallated phosphorescent materials also include compoundsaccording to formula (J) wherein the monoanionic bidentate ligand X—Y isanother C,N-cyclometallating ligand. Examples includebis(1-phenylisoquinolinato-N,C^(2′))(2-phenylpyridinato-N,C^(2′))Iridium(III)and bis(2-phenylpyridinato-N,C^(2′))(1-phenylisoquinolinato-N,C^(2′))Iridium(III). Synthesis of suchtris-C,N-cyclometallated complexes containing two differentC,N-cyclometallating ligands may be conveniently synthesized by thefollowing steps. First, a bis-C,N-cyclometallated diiridium dihalidecomplex (or analogous dirhodium complex) is made according to the methodof Nonoyama (Bull. Chem. Soc. Jpn., 47, 767 (1974)). Secondly, a zinccomplex of the second, dissimilar C,N-cyclometallating ligand isprepared by reaction of a zinc halide with a lithium complex or Grignardreagent of the cyclometallating ligand. Third, the thus formed zinccomplex of the second C,N-cyclometallating ligand is reacted with thepreviously obtained bis-C,N-cyclometallated diiridium dihalide complexto form a tris-C,N-cyclometallated complex containing the two differentC,N-cyclometallating ligands. Desirably, the thus obtainedtris-C,N-cyclometallated complex containing the two differentC,N-cyclometallating ligands may be converted to an isomer wherein the Catoms bonded to the metal (e.g. Ir) are all mutually cis by heating in asuitable solvent such as dimethyl sulfoxide.

Suitable phosphorescent materials according to formula (J) may inaddition to the C,N-cyclometallating ligand(s) also contain monoanionicbidentate ligand(s) X—Y that are not C,N-cyclometallating. Commonexamples are beta-diketonates such as acetylacetonate, and Schiff basessuch as picolinate. Examples of such mixed ligand complexes according toformula (J) includebis(2-phenylpyridinato-N,C^(2′))Iridium(III)(acetylacetonate),bis(2-(2′-benzothienyl)pyridinato-N,C^(3′))Iridium(III)(acetylacetonate),andbis(2-(4′,6′-difluorophenyl)-pyridinato-N,C^(2′))Iridium(III)(picolinate).

Other important phosphorescent materials according to formula (J)include C,N-cyclometallated Pt(II) complexes such ascis-bis(2-phenylpyridinato-N,C^(2′))platinum(II),cis-bis(2-(2′-thienyl)pyridinato-N,C^(3′)) platinum(II),cis-bis(2-(2′-thienyl)quinolinato-N,C^(5′)) platinum(II), or(2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)) platinum (II)(acetylacetonate).

The emission wavelengths (color) of C,N-cyclometallated phosphorescentmaterials according to formula (J) are governed principally by thelowest energy optical transition of the complex and hence by the choiceof the C,N-cyclometallating ligand. For example, 2-phenyl-pyridinato-NC^(2′) complexes are typically green emissive while1-phenyl-isoquinolinolato-N,C^(2′) complexes are typically red emissive.In the case of complexes having more than one C,N-cyclometallatingligand, the emission will be that of the ligand having the property oflongest wavelength emission. Emission wavelengths may be further shiftedby the effects of substituent groups on the C,N-cyclometallatingligands. For example, substitution of electron donating groups atappropriate positions on the N-containing ring A or electron acceptinggroups on the C-containing ring B tend to blue-shift the emissionrelative to the unsubstituted C,N-cyclometallated ligand complex.Selecting a monodentate anionic ligand X,Y in formula (J) having moreelectron accepting properties also tends to blue-shift the emission of aC,N-cyclometallated ligand complex. Examples of complexes having bothmonoanionic bidentate ligands possessing electron accepting propertiesand electron accepting substituent groups on the C-containing ring Bincludebis(2-(4′,6′-difluorophenyl)-pyridinato-N,C^(2′))iridium(III)(picolinate)andbis(2-(4′,6′-difluorophenyl)-pyridinato-N,C^(2′))iridium(III)(tetrakis(1-pyrazolyl)borate).

The central metal atom in phosphorescent materials according to formula(J) may be Rh or Ir (m+n=3) and Pd or Pt (m+n=2). Preferred metal atomsare Ir and Pt since they tend to give higher phosphorescent quantumefficiencies according to the stronger spin-orbit coupling interactionsgenerally obtained with elements in the third transition series.

In addition to bidentate C,N-cyclometallating complexes represented byformula (J), many suitable phosphorescent materials contain multidentateC,N-cyclometallating ligands. Phosphorescent materials having tridentateligands suitable for use in the present invention are disclosed in U.S.Pat. No. 6,824,895 B1 and references therein, incorporated in theirentirety herein by reference. Phosphorescent materials havingtetradentate ligands suitable for use in the present invention aredescribed by the following formulae:

wherein:

-   -   M is Pt or Pd;    -   R¹-R⁷ represent hydrogen or independently selected substituents,        provided that R¹ and R², R² and R³, R³ and R⁴, R⁴ and R⁵, R⁵ and        R⁶, as well as R⁶ and R⁷ may join to form a ring group;    -   R⁸-R¹⁴ represent hydrogen or independently selected        substituents, provided that R⁸ and R⁹, R⁹ and R¹⁰, R¹⁰ and R¹¹,        R¹¹ and R¹², R¹² and R¹³, as well as R¹³ and R¹⁴, may join to        form a ring group;    -   E represents a bridging group selected from the following:

wherein:

-   -   R and R′ represent hydrogen or independently selected        substituents; provided R and R′ may combine to form a ring        group.

One desirable tetradentate C,N-cyclometallated phosphorescent materialsuitable for use in as the phosphorescent dopant is represented by thefollowing formula:

wherein:

-   -   R¹-R⁷ represent hydrogen or independently selected substituents,        provided that R¹ and R², R² and R³, R³ and R⁴, R⁴ and R⁵, R⁵ and        R⁶, as well as R⁶ and R⁷ may combine to form a ring group;    -   R⁸-R¹⁴ represent hydrogen or independently selected        substituents, provided that R⁸ and R⁹, R⁹ and R¹⁰, R¹⁰ and R¹¹,        R¹¹ and R¹², R¹² and R¹³, as well as R¹³ and R¹⁴ may combine to        form a ring group;    -   Z¹-Z⁵ represent hydrogen or independently selected substituents,        provided that Z¹ and Z², Z² and Z³, Z³ and Z⁴, as well as Z⁴ and        Z⁵ may combine to form a ring group.

Specific examples of phosphorescent materials having tetradentateC,N-cyclometallating ligands suitable for use in the present inventioninclude compounds (M-1), (M-2) and (M-3) represented below.

Phosphorescent materials having tetradentate C,N-cyclometallatingligands may be synthesized by reacting the tetradentateC,N-cyclometallating ligand with a salt of the desired metal, such asK₂PtCl₄, in a proper organic solvent such as glacial acetic acid to formthe phosphorescent material having tetradentate C,N-cyclometallatingligands. A tetraalkylammonium salt such as tetrabutylammonium chloridecan be used as a phase transfer catalyst to accelerate the reaction.

Other phosphorescent materials that do not involve C,N-cyclometallatingligands are known. Phosphorescent complexes of Pt(II), Ir(I), and Rh(I)with maleonitriledithiolate have been reported (Johnson et al., J. Am.Chem. Soc., 105,1795 (1983)). Re(I) tricarbonyl diimine complexes arealso known to be highly phosphorescent (Wrighton and Morse, J. Am. Chem.Soc., 96, 998 (1974); Stufkens, Comments Inorg. Chem., 13, 359 (1992);Yam, Chem. Commun., 789 (2001)). OS(II) complexes containing acombination of ligands including cyano ligands and bipyridyl orphenanthroline ligands have also been demonstrated in a polymer OLED (Maet al., Synthetic Metals, 94, 245 (1998)).

Porphyrin complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(IT) are also useful phosphorescent dopant.

Still other examples of useful phosphorescent materials includecoordination complexes of the trivalent lanthanides such as Tb³⁺ andEu³⁺ (Kido et al., Chem. Lett., 657 (1990); J. Alloys and Compounds,192, 30 (1993); Jpn. J. Appl. Phys., 35, L394 (1996) and Appl. Phys.Lett., 65, 2124 (1994)).

The phosphorescent dopant in a phosphorescent LEL is typically presentin an amount of 50% or less; 25% or less, most typically in the range of0.5% to 15% with the most desirable range being from 1% to 12%. In someembodiments, the phosphorescent dopant(s) may be attached to one or morehost materials. The host materials may further be polymers. Thethickness of a phosphorescent LEL is greater than 0.5 nm, preferably, inthe range of from 1.0 nm to 40 nm.

b) Fluorescent Light Emitting Layers

Although the term “fluorescent” is commonly used to describe anylight-emitting material, in this case it refers to a material that emitslight from a singlet excited state. In mixed or hybrid systems,fluorescent materials may be used in adjacent layers, in adjacentpixels, or any combination with the phosphorescent material, Care mustbe taken not to select materials that will adversely affect theperformance of the phosphorescent materials of this invention. Oneskilled in the art will understand that concentrations and tripletenergies of fluorescent materials in an adjacent layer must beappropriately set so as to prevent unwanted quenching of thephosphorescence.

Typically, a fluorescent LEL includes at least one host and at least onefluorescent dopant. The host may be a hole-transporting material or anyof the suitable hosts for phosphorescent dopants as defined above or maybe an electron-transporting material as defined below.

The dopant is typically chosen from highly fluorescent dyes, e.g.,transition metal complexes as described in WO 98/55561 A1, WO 00/18851A1, WO 00157676 A1, and WO 00/70655.

Some fluorescent emitting materials include, but are not limited to,derivatives of anthracene, tetracene, xanthene, perylene, rubrene,coumarin, rhodamine, and quinacridone, dicyanomethylenepyran compounds,thiopyran compounds, polymethine compounds, pyryliurn and thiapyryliumcompounds, fluorene derivatives, periflanthene derivatives,indenoperylene derivatives, bis(azinyl)amine boron compounds,bis(azinyl)methane compounds (as described in U.S. Pat. No. 5,121,029)and carbostyryl compounds. Illustrative examples of useful materialsinclude, but are not limited to, the following:

FD-1 FD-2 FD-3

FD-4 FD-5

FD-6 FD-7

FD-8

X R1 R2 FD-9 O H H FD-10 O H Methyl FD-11 O Methyl H FD-12 O MethylMethyl FD-13 O H t-butyl FD-14 O t-butyl H FD-15 O t-butyl t-butyl FD-16S H H FD-17 S H Methyl FD-18 S Methyl H FD-19 S Methyl Methyl FD-20 S Ht-butyl FD-21 S t-butyl H FD-22 S t-butyl t-butyl

X R1 R2 FD-13 O H H FD-24 O H Methyl FD-25 O Methyl H FD-26 O MethylMethyl FD-27 O H t-butyl FD-28 O t-butyl H FD-29 O t-butyl t-butyl FD-30S H H FD-31 S H Methyl FD-32 S Methyl H FD-33 S Methyl Methyl FD-34 S Ht-butyl FD-35 S t-butyl H FD-36 S t-butyl t-butyl

R FD-37 phenyl FD-38 methyl FD-39 t-butyl FD-40 mesityl

R FD-41 phenyl FD-42 methyl FD-43 t-butyl FD-44 mesityl

FD-45

FD-46

FD-47 FD-48

FD-49 FD-50

FD-51 FD-52

FD-53 FD-54

FD-55

FD-56

FD-57

Preferred fluorescent blue dopants may be found in Chen, Shi, and Tang,“Recent Developments in Molecular Organic Electroluminescent Materials,”Macromol. Symp. 125, 1 (1997) and the references cited therein; Hung andChen, “Recent Progress of Molecular Organic Electroluminescent Materialsand Devices,” Mat. Sci. and Eng. R39, 143 (2002) and the referencescited therein.

A particularly preferred class of blue-emitting fluorescent dopants isrepresented by Formula (N), known as a bis(azinyl)amine borane complex,and is described in U.S. Pat. No. 6,661,023.

wherein:

-   -   A and A′ represent independent azine ring systems corresponding        to 6-membered aromatic ring systems containing at least one        nitrogen;    -   each X^(a) and X^(b) is an independently selected substituent,        two of which may join to form a fused ring to A or A′;    -   m and n are independently 0 to 4;    -   Z^(a) and Z^(b) are independently selected substituents; and    -   1, 2, 3, 4, 1′, 2′, 3′, and 4′ are independently selected as        either carbon or nitrogen atoms.

Desirably, the azine rings are either quinolinyl or isoquinolinyl ringssuch that 1, 2, 3, 4, 1′, 2′, 3′, and 4′ are all carbon; m and n areequal to or greater than 2; and X^(a) and X^(b) represent at least twocarbon substituents which join to form an aromatic ring. Desirably,Z^(a) and Z^(b) are fluorine atoms.

Preferred embodiments further include devices where the two fused ringsystems are quinoline or isoquinoline systems; the aryl or heterocyclicsubstituent is a phenyl group; there are present at least two X^(a)groups and two X^(b) groups which join to form a 6-6 fused ring, thefused ring systems are fused at the 1-2, 3-4,1′-2′, or 3′-4′ positions,respectively; one or both of the fused rings is substituted by a phenylgroup; and where the dopant is depicted in Formulae (N-a), (N-b), or(N-c).

wherein:

-   -   each X^(c), X^(d), X^(e), X^(f), X^(g), and X^(h) is hydrogen or        an independently selected substituent, one of which must be an        aryl or heterocyclic group.

Desirably, the azine rings are either quinolinyl or isoquinolinyl ringssuch that 1, 2, 3, 4, 1′, 2′, 3′, and 4′ are all carbon; m and n areequal to or greater than 2; and X^(a) and X^(b) represent at least twocarbon substituents which join to form an aromatic ring, and one is anaryl or substituted aryl group. Desirably, Z^(a) and Z^(b) are fluorineatoms.

Of these, compound FD-54 is particularly useful.

Coumarins represent a useful class of green-emitting dopants asdescribed by Tang et al. in U.S. Pat. Nos. 4,769,292 and 6,020,078.Green dopants or light-emitting materials can be coated as 0.01 to 50%by weight into the host material, but typically coated as 0.01 to 30%and more typically coated as 0.01 to 15% by weight into the hostmaterial. Examples of useful green-emitting coumarins include C545T andC545TB. Quinacridones represent another useful class of green-emittingdopants. Useful quinacridones are described in U.S. Pat. No. 5,593,788,publication JP 09-13026A, and commonly assigned U.S. patent applicationSer. No. 10/184,356 filed Jun. 27, 2002 by Lelia Cosimbescu, entitled“Device Containing Green Organic Light-Emitting Diode”, the disclosureof which is incorporated herein.

Examples of particularly useful green-emitting quinacridones are FD-7and FD-8.

Formula (N-d) below represents another class of green-emitting dopantsusefull in the invention.

wherein:

-   -   A and A′ represent independent azine ring systems corresponding        to 6-membered aromatic ring systems containing at least one        nitrogen;    -   each X^(a) and X^(b) is an independently selected substituent,        two of which may join to form a fused ring to A or A′;    -   m and n are independently 0 to 4;    -   Y is H or a substituent;    -   Z^(a) and Z^(b) are independently selected substituents; and    -   1, 2, 3, 4, 1′, 2′, 3′, and 4′ are independently selected as        either carbon or nitrogen atoms.

In the device, 1, 2, 3, 4, 1′, 2′, 3′, and 4′ are conveniently allcarbon atoms. The device may desirably contain at least one or both ofring A or A′ that contains substituents joined to form a fused ring. Inone useful embodiment, there is present at least one X^(a) or X^(b)group selected from the group consisting of halide and alkyl, aryl,alkoxy, and aryloxy groups. In another embodiment, there is present aZ^(a) and Z^(b) group independently selected from the group consistingof fluorine and alkyl, aryl, alkoxy and aryloxy groups. A desirableembodiment is where Z^(a) and Z^(b) are F. Y is suitably hydrogen or asubstituent such as an alkyl, aryl, or heterocyclic group.

The emission wavelength of these compounds may be adjusted to someextent by appropriate substitution around the central bis(azinyl)metheneboron group to meet a color aim, namely green. Some examples of usefulmaterial are FD-50, FD-51 and FD-52.

Naphthacenes and derivatives thereof also represent a useful class ofemitting dopants, which can also be used as stabilizers. These dopantmaterials can be coated as 0.01 to 50% by weight into the host material,but typically coated as 0.01 to 30% and more typically coated as 0.01 to15% by weight into the host material. Naphthacene derivative YD-1(t-BuDPN) below, is an example of a dopant material used as astabilizer.

Some examples of this class of materials are also suitable as hostmaterials as well as dopants. For example, see U.S. Pat. Nos. 6,773,832or 6,720,092. A specific example of this would be rubrene (FD-S).

Another class of useful dopants are perylene derivatives; for examplesee U.S. Pat. No. 6,689,493. A specific example is FD-46.

Metal complexes of 8-hydroxyquinoline and similar derivatives (FormulaO) constitute one class of useful non-electroluminescent host compoundscapable of supporting electroluminescence, and are particularly suitablefor light emission of wavelengths longer than 500 nm, e.g., green,yellow, orange, and red.

wherein:

-   -   M represents a metal;    -   n is an integer of from 1 to 4; and    -   Z independently in each occurrence represents the atoms        completing a nucleus having at least two fused aromatic rings.

From the foregoing it is apparent that the metal can be monovalent,divalent, trivalent, or tetravalent metal. The metal can, for example,be an alkali metal, such as lithium, sodium, or potassium; an alkalineearth metal, such as magnesium or calcium; an earth metal, such asaluminum or gallium, or a transition metal such as zinc or zirconium.Generally any monovalent, divalent, trivalent, or tetravalent metalknown to be a useful chelating metal can be employed.

Z completes a heterocyclic nucleus containing at least two fusedaromatic rings, at least one of which is an azole or azine ring.Additional rings, including both aliphatic and aromatic rings, can befused with the two required rings, if required. To avoid addingmolecular bulk without improving on function the number of ring atoms isusually maintained at 18 or less.

Illustrative of useful chelated oxinoid compounds are the following:

-   -   O-1: Aluminum trisoxine [alias,        tris(8-quinolinolato)aluminum(III)]    -   O-2: Magnesium bisoxine [alias,        bis(8-quinolinolato)magnesium(II)]    -   O-3: Bis[benzo{f}-8-quinolinolato]zinc (II)    -   O-4:        Bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato)        aluminum(III)    -   O-5: Indium trisoxine [alias, tris(8-quinolinolato)indium]    -   O-6: Aluminum tris(5-methyloxine) [alias,        tris(5-methyl-8-quinolinolato) aluminum(III)]    -   O-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)]    -   O-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)]    -   O-9: Zirconium oxine [alias,        tetra(8-quinolinolato)zirconium(IV)]    -   O-10: Bis(2-methyl-8-quinolinato)-4-phenylphenolatoaluminum        (III)

Anthracene derivatives according to formula (P) are also very usefulhost materials in the LEL:

wherein:

-   -   R₁-R₁₀ are independently chosen from hydrogen, alkyl groups from        1-24 carbon atoms or aromatic groups from 1-24 carbon atoms.        Particularly preferred are compounds where R₁ and R₆ are phenyl,        biphenyl or naphthyl, R₃ is phenyl, substituted phenyl or        naphthyl and R₂, R₄, R₅, R₇-R₁₀ are all hydrogen. Such        anthracene hosts are known to have excellent electron        transporting properties.

Particularly desirable are derivatives of9,10-di-(2-naphthyl)anthracene. Illustrative examples include9,10-di-(2-naphthyl)anthracene (ADN) and2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN). Other anthracenederivatives can be useful as a non-electroluminescent compound in theLEL, such as diphenylanthracene and its derivatives, as described inU.S. Pat. No. 5,927,247. Styrylarylene derivatives as described in U.S.Pat. No. 5,121,029 and JP 08333569 are also usefulnon-electroluminescent materials. For example,9,10-bis[4-(2,2-diphenylethenyl)phenyl]anthracene,4,4′-Bis(2,2-diphenylethenyl)-1,1′-biphenyl (DPVBi) and phenylanthracenederivatives as described in EP 681,019 are useful non-electroluminescentmaterials.

Some illustrative examples of suitable anthracenes are:

Another useful class of host materials, particularly for a red-emittinglayer, is naphthacenes including rubrene derivatives.

Spacer Layer

Spacer layers, when present, are located in direct contact to a LEL.They may be located on either the anode or cathode side, or even bothsides of the LEL. They typically do not contain any light-emissivedopants. One or more materials may be used and could be either ahole-transporting material as defined above or an electron-transportingmaterial as defined below. If located next to a phosphorescent LEL, thematerial in the spacer layer should have a triplet energy about equal toor greater than that of the host material in the phosphorescent LEL.Most desirably, the material in the spacer layer will be the same asused as the host in the adjacent LEL. Thus, any of the host materialsdescribed as also suitable for use in a spacer layer. The spacer layershould be thin; at least 0.1 nm, but preferably in the range of from 1.0nm to 20 nm.

Hole-Blocking Layer (HBL)

When a LEL containing a phosphorescent emitter is present, it isdesirable to locate a hole-blocking layer 135 between theelectron-transporting layer 136 and the light-emitting layer 134 to helpconfine the excitons and recombination events to the LEL. In this case,there should be an energy barrier for hole migration from co-hosts intothe hole-blocking layer, while electrons should pass readily from thehole-blocking layer into the light-emitting layer comprising co-hostmaterials and a phosphorescent emitter. It is further desirable that thetriplet energy of the hole-blocking material be greater than that of thephosphorescent material. Suitable hole-blocking materials are describedin WO 00/70655A2, WO 01/41512 and WO 01/93642 A1. Two examples of usefulhole-blocking materials are bathocuproine (BCP) andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq).Metal complexes other than BAlq are also known to block holes andexcitons as described in US 20030068528. When a hole-blocking layer isused, its thickness can be between 2 and 100 nm and suitably between 5and 10 nm.

Electron Transporting Layer

The purpose of an electron-transporting layer is to allow efficientmovement of electrons from the cathode to the LEL. As such, it does notemit substantial amounts of light.

Polycyclic aromatic hydrocarbons (PAH) are often very useful in the ETL.Examples of desirable polycyclic aromatic hydrocarbons in this inventionare anthracenes, fluoranthenes and naphthacenes including rubrenederivatives.

The anthracene electron transporting derivatives are represented byFormula (P) as described above in connection with host materials for aLEL. The anthracene in the ETL can be the same or different from thatused in the LEL.

In addition to any of the electron-transporting materials previouslydescribed, any other materials known to be suitable for use in the ETLmay be used. Included are, but are not limited to, chelated oxinoidcompounds, anthracene derivatives, pyridine-based materials, imidazoles,oxazoles, thiazoles and their derivatives, polybenzobisazoles,cyano-containing polymers and perfluorinated materials. Otherelectron-transporting materials include various butadiene derivatives asdisclosed in U.S. Pat. No. 4,356,429 and various heterocyclic opticalbrighteners as described in U.S. Pat. No. 4,539,507.

A preferred class of benzazoles is described by Shi et al. in U.S. Pat.Nos. 5,645,948 and 5,766,779. Such compounds are represented bystructural formula (Q):

-   -   In formula (Q), n is selected from 2 to 8 and i is selected from        1-5;    -   Z is independently O, NR or S;    -   R is individually hydrogen; alkyl of from 1 to 24 carbon atoms,        for example, propyl, t-butyl, heptyl, and the like; aryl or        hetero-atom substituted aryl of from 5 to 20 carbon atoms, for        example, phenyl and naphthyl, furyl, thienyl, pyridyl,        quinolinyl and other heterocyclic systems; or halo such as        chloro, fluoro; or atoms necessary to complete a fused aromatic        ring; and    -   X is a linkage unit consisting of carbon, alkyl, aryl,        substituted alkyl, or substituted aryl, which conjugately or        unconjugately connects the multiple benzazoles together.

An example of a useful benzazole is2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI)represented by a formula (Q-1) shown below:

Another suitable class of the electron-transporting materials includesvarious substituted phenanthrolines as represented by formula (R):

In formula (R), R₁-R₈ are independently hydrogen, alkyl group, aryl orsubstituted ayl group, and at least one of R₁-R₈ is aryl group orsubstituted aryl group.

Examples of suitable materials are2,9-dimethyl-4,7-diphenyl-phenanthroline (BCP) (see formula (R-1)) and4,7-diphenyl-1,10-phenanthroline (Bphen) (see formula (R-2)).

Suitable triarylboranes that function as an electron-transportingmaterial may be selected from compounds having the chemical formula (S):

wherein:

-   -   Ar₁ to Ar₃ are independently an aromatic hydrocarbocyclic group        or an aromatic heterocyclic group which may have a substituent.        It is preferable that compounds having the above structure are        selected from formula (S-1):

wherein:

-   -   R₁-R₁₅ are independently hydrogen, fluoro, cyano,        trifluoromethyl, sulfonyl, alkyl, aryl or substituted aryl        group.    -   Specific representative embodiments of the triarylboranes        include:

The electron-transporting material may also be selected from substituted1,3,4-oxadiazoles of formuta (T):

wherein:

-   -   R₁ and R₂ are individually hydrogen; alkyl of from 1 to 24        carbon atoms, for example, propyl, t-butyl, heptyl, and the        like; aryl or hetero-atom substituted aryl of from 5 to 20        carbon atoms, for example, phenyl and naphthyl, furyl, thienyl,        pyridyl, quinolinyl and other heterocyclic systems; or halo such        as chloro, fluoro; or atoms necessary to complete a fused        aromatic ring.

Illustrative of the useful substituted oxadiazoles are the following:

The electron-transporting material may also be selected from substituted1,2,4-triazoles according to formula (U):

wherein:

-   -   R₁, R₂ and R₃ are independently hydrogen, alkyl group, aryl or        substituted aryl group, and at least one of R₁-R₃ is aryl group        or substituted aryl group. An example of a useful triazole is        3-phenyl-4-(1-naphtyl)-5-phenyl-1,2,4-triazole represented by        formula (U-1):

The electron-transporting material may also be selected from substituted1,3,5-triazines. Examples of suitable materials are:

-   -   2,4,6-tris(diphenylamino)-1,3,5-triazine;    -   2,4,6-tricarbazolo-1,3,5-triazine;    -   2,4,6-tris(N-phenyl-2-naphthylamino)-1,3,5-triazine;    -   2,4,6-tris(N-phenyl-1-naphthylamino)-1,3,5-triazine;    -   4,4′,6,6′-tetraphenyl-2,2′-bi-1,3,5-triazine;    -   2,4,6-tris([1,1′:3′,1″-terphenyl]-5′-yl)-1,3,5-triazine.

In addition, any of the metal chelated oxinoid compounds includingchelates of oxine itself (also commonly referred to as 8-quinolinol or8-hydroxyquinoline) of Formula (O) useful as host materials in a LEL arealso suitable for use in the ETL.

Some metal chelated oxinoid compounds having high triplet energy can beparticularly useful as an electron-transporting materials. Particularlyuseful aluminum or gallium complex materials with high triplet energylevels are represented by Formula (V).

In Formula (V), M₁ represents Al or Ga. R₂-R₇ represent hydrogen or anindependently selected substituent. Desirably, R₂ represents anelectron-donating group. Suitably, R₃ and R₄ each independentlyrepresent hydrogen or an electron donating substituent. A preferredelectron-donating group is alkyl such as methyl. Preferably, R₅, R₆, andR₇ each independently represent hydrogen or an electron-accepting group.Adjacent substituents, R₂-R₇, may combine to form a ring group. L is anaromatic moiety linked to the aluminum by oxygen, which may besubstituted with substituent groups such that L has from 6 to 30 carbonatoms.

Illustrative of useful chelated oxinoid compounds for use in the ETL isAluminum(III) bis(2-methyl-8-hydroxyquinoline)-4-phenylphenolate [alias,Balq]. These materials are also suitable for use as hosts forphosphorescent light-emitting materials.

The thickness of the ETL is in the range of from 5 nm to 200 nm,preferably, in the range of from 10 nm to 150 nm.

Electron Injection Layer

The EIL 138 is typically located adjacent to the cathode and helps tofacilitate movement of electrons from the cathode into the other organiclayers. The EIL may be composed only of one material or multiplematerials and may be subdivided into sublayers. There may beintermediate layers between any of these 3 interfaces; for example, athin layer of LiF between the cathode and the EIL.

The EIL may be an n-type doped layer containing at least oneelectron-transporting material as a host and at least one n-type dopant.The dopant is capable of reducing the host by charge transfer. The term“n-type doped layer” means that this layer has semiconducting propertiesafter doping, and the electrical current through this layer issubstantially carried by the electrons.

The host in the EIL may be an electron-transporting material capable ofsupporting electron injection and electron transport. Theelectron-transporting material can be selected from theelectron-transporting materials for use in the ETL region as definedabove. Phenanthrolines are particularly suitable for this use.

The n-type dopant in the n-type doped EIL may be is selected from alkalimetals, alkali metal compounds, alkaline earth metals, or alkaline earthmetal compounds, or combinations thereof. The term “metal compounds”includes organometallic complexes, metal-organic salts, and inorganicsalts, oxides and halides. Among the class of metal-containing n-typedopants, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Sm, Eu, Th, Dy, orYb, and their compounds, are particularly useful. The materials used asthe n-type dopants in the n-type doped EIL also include organic reducingagents with strong electron-donating properties. By “strongelectron-donating properties” it is meant that the organic dopant shouldbe able to donate at least some electronic charge to the host to form acharge-transfer complex with the host. Nonlimiting examples of organicmolecules include bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF),tetrathiafulvalene (TTF), and their derivatives. In the case ofpolymeric hosts, the dopant is any of the above or also a materialmolecularly dispersed or copolymerized with the host as a minorcomponent. Preferably, the n-type dopant in the n-type doped EILincludes Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Nd, Sm, Eu, Th, Dy,or Yb, or combinations thereof. Lithium is preferred. The n-type dopedconcentration is preferably in the range of 0.01-20% by volume of thislayer.

Another material suitable for an EIL is an organic alkali metalcompound. These organic alkali metal compounds are also suitable for usein the ETL as well as the BIL.

The EIL may be composed only of a single organic alkali metal compoundor may be a mixture of 2 or more organic alkali metal compounds. Inaddition to the alkali metal compounds, the EIL may also contain one ormore polycyclic aromatic hydrocarbons. The % volume ratio of organicalkali metal compound to additional material can be anywhere from 1% to99%, more suitably 10% to 90% and most desirably, 30 to 70%. Thethickness of the EIL can be 0.1 nm to 20 nm in thickness, but preferably0.4 nm to 10 nm, and more preferable from 1 nm to 8 nm.

The alkali metal used in the compounds of the invention belongs to Group1 of the periodic table. Of these, lithium is highly preferred.

Organic lithium compounds (electron injection material or EIM) useful inthe invention are according to Formula (IV):(Li⁺)_(m)(Q)_(n)  Formula (IV)wherein:

-   -   Q is an anionic organic ligand; and    -   m and n are independently selected integers selected to provide        a neutral charge on the complex.

The anionic organic ligand Q is most suitably monoanionic and containsat least one ionizable site consisting of oxygen, nitrogen or carbon. Inthe case of enolates or other tautomeric systems containing oxygen, itwill be considered and drawn with the lithium bonded to the oxygenalthough the lithium may in fact be bonded elsewhere to form a chelate.It is also desirable that the ligand contains at least one nitrogen atomthat can form a coordinate or dative bond with the lithium. The integersm and n can be greater than 1 reflecting a known propensity for someorganic lithium compounds to form cluster complexes.

In another embodiment, Formula (V) represents the EIM.

wherein:

-   -   Z and the dashed arc represent two to four atoms and the bonds        necessary to complete a 5- to 7-membered ring with the lithium        cation;    -   each A represents hydrogen or a substituent and each B        represents hydrogen or an independently selected substituent on        the Z atoms, provided that two or more substituents may combine        to form a fused ring or a fused ring system; and    -   j is 0-3 and k is 1 or 2; and    -   m and n are independently selected integers selected to provide        a neutral charge on the complex.

It is most desirable that the A and B substituents of Formula (V)together form an additional ring system. This additional ring system mayfurther contain additional heteroatoms to form a multidentate ligandwith coordinate or dative bonding to the lithium. Desirable heteroatomsare nitrogen or oxygen.

In Formula (V), it is preferred that the oxygen shown is part of ahydroxyl, carboxy or keto group. Examples of suitable nitrogen ligandsare 8-hydroxyquinoline, 2-hydroxymethylpyridine, pipecolinic acid or2-pyridinecarboxylic acid.

Specific examples of useful electron injecting materials are as follows:

When the EIL is composed only of the organic lithium compound of theinvention, the thickness of the EIL is typically less than 20 nm, butpreferably 0.4 nm to 10 nm, and more preferable from 1 nm to 8 nm. Whenan n-type doped EIL is employed, the thickness is typically less than200 nm, and preferably in the range of less than 150 nm.

Cathode

When light emission is viewed solely through the anode, the cathode 140includes nearly any conductive material. Desirable materials haveeffective film-forming properties to ensure effective contact with theunderlying organic layer, promote electron injection at low voltage, andhave effective stability. Useful cathode materials often contain a lowwork function metal (<4.0 eV) or metal alloy. One preferred cathodematerial includes a Mg:Ag alloy as described in U.S. Pat. No. 4,885,221.Another suitable class of cathode materials includes bilayers includinga thin inorganic EIL in contact with an organic layer (e.g., organic EILor ETL), which is capped with a thicker layer of a conductive metal.Here, the inorganic EIL preferably includes a low work function metal ormetal salt and, if so, the thicker capping layer does not need to have alow work function. One such cathode includes a thin layer of LiFfollowed by a thicker layer of A1 as described in U.S. Pat. No.5,677,572. Other useful cathode material sets include, but are notlimited to, those disclosed in U.S. Pat. Nos. 5,059,861, 5,059,862, and6,140,763.

When light emission is viewed through the cathode, cathode 140 should betransparent or nearly transparent. For such applications, metals shouldbe thin or one should use transparent conductive oxides, or includethese materials. Optically transparent cathodes have been described inmore detail in U.S. Pat. Nos. 4,885,211, 5,247,190, 5,703,436,5,608,287, 5,837,391, 5,677,572, 5,776,622, 5,776,623, 5,714,838,5,969,474, 5,739,545, 5,981,306, 6,137,223, 6,140,763, 6,172,459,6,278,236, 6,284,393, and EP 1 076 368. Cathode materials are typicallydeposited by thermal evaporation, electron beam evaporation, ionsputtering, or chemical vapor deposition. When needed, patterning isachieved through many well known methods including, but not limited to,through-mask deposition, integral shadow masking, for example asdescribed in U.S. Pat. No. 5,276,380 and EP 0 732 868, laser ablation,and selective chemical vapor deposition.

Substrate

OLED 100 is typically provided over a supporting substrate 110 whereeither the anode 120 or cathode 140 can be in contact with thesubstrate. The electrode in contact with the substrate is convenientlyreferred to as the bottom electrode. Conventionally, the bottomelectrode is the anode 120, but this invention is not limited to thatconfiguration. The substrate can either be light transmissive or opaque,depending on the intended direction of light emission. The lighttransmissive property is desirable for viewing the EL emission throughthe substrate. Transparent glass or plastic is commonly employed in suchcases. The substrate can be a complex structure comprising multiplelayers of materials. This is typically the case for active matrixsubstrates wherein TFTs are provided below the OLED layers. It is stillnecessary that the substrate, at least in the emissive pixelated areas,be comprised of largely transparent materials such as glass or polymers.For applications where the EL emission is viewed through the topelectrode, the transmissive characteristic of the bottom support isimmaterial, and therefore the substrate can be light transmissive, lightabsorbing or light reflective. Substrates for use in this case include,but are not limited to, glass, plastic, semiconductor materials such assilicon, ceramics, and circuit board materials. Again, the substrate canbe a complex structure comprising multiple layers of materials such asfound in active matrix TFT designs. It is necessary to provide in thesedevice configurations a light-transparent top electrode.

Deposition of Organic Layers

The organic materials mentioned above are suitably deposited throughsublimation, but can be deposited from a solvent with an optional binderto improve film formation. If the material is a polymer, solventdeposition is usually preferred. The material to be deposited bysublimation can be vaporized from a sublimator “boat” often comprised ofa tantalum material, e.g., as described in U.S. Pat. No. 6,237,529, orcan be first coated onto a donor sheet and then sublimed in closerproximity to the substrate. Layers with a mixture of materials canutilize separate sublimator boats or the materials can be pre-mixed andcoated from a single boat or donor sheet. Patterned deposition can beachieved using shadow masks, integral shadow masks (U.S. Pat. No.5,294,870), spatially-defined thermal dye transfer from a donor sheet(U.S. Pat. Nos. 5,851,709 and 6,066,357) and inkjet method (U.S. Pat.No. 6,066,357).

Organic materials useful in making OLEDs, for example organichole-transporting materials, organic light-emitting materials doped withan organic electroluminescent components have relatively complexmolecular structures with relatively weak molecular bonding forces, sothat care must be taken to avoid decomposition of the organicmaterial(s) during physical vapor deposition. The aforementioned organicmaterials are synthesized to a relatively high degree of purity, and areprovided in the form of powders, flakes, or granules. Such powders orflakes have been used heretofore for placement into a physical vapordeposition source wherein heat is applied for forming a vapor bysublimation or vaporization of the organic material, the vaporcondensing on a substrate to provide an organic layer thereon.

Several problems have been observed in using organic powders, flakes, orgranules in physical vapor deposition: These powders, flakes, orgranules are difficult to handle. These organic materials generally havea relatively low physical density and undesirably low thermalconductivity, particularly when placed in a physical vapor depositionsource which is disposed in a chamber evacuated to a reduced pressure aslow as 10⁻⁶ Torr. Consequently, powder particles, flakes, or granulesare heated only by radiative heating from a heated source, and byconductive heating of particles or flakes directly in contact withheated surfaces of the source. Powder particles, flakes, or granuleswhich are not in contact with heated surfaces of the source are noteffectively heated by conductive heating due to a relatively lowparticle-to-particle contact area; This can lead to nonuniform heatingof such organic materials in physical vapor deposition sources.Therefore, result in potentially nonuniform vapor-deposited organiclayers formed on a substrate.

These organic powders can be consolidated into a solid pellet. Thesesolid pellets consolidating into a solid pellet from a mixture of asublimable organic material powder are easier to handle. Consolidationof organic powder into a solid pellet can be accomplished withrelatively simple tools. A solid pellet formed from mixture comprisingone or more non-luminescent organic non-electroluminescent componentmaterials or luminescent electroluminescent component materials ormixture of non-electroluminescent component and electroluminescentcomponent materials can be placed into a physical vapor depositionsource for making organic layer. Such consolidated pellets can be usedin a physical vapor deposition apparatus.

In one aspect, the present invention provides a method of making anorganic layer from compacted pellets of organic materials on asubstrate, which will form part of an OLED.

One preferred method for depositing the materials of the presentinvention is described in US 2004/0255857 and U.S. Ser. No. 10/945,941where different source evaporators are used to evaporate each of thematerials of the present invention. A second preferred method involvesthe use of flash evaporation where materials are metered along amaterial feed path in which the material feed path is temperaturecontrolled. Such a preferred method is described in the followingco-assigned patent applications: U.S. Ser. No. 10/784,585; U.S. Ser. No.10/805,980; U.S. Ser. No. 10/945,940; U.S. Ser. No. 10/945,941; U.S.Ser. No. 11/050,924; and U.S. Ser. No. 11/050,934. Using this secondmethod, each material may be evaporated using different sourceevaporators or the solid materials may be mixed prior to evaporationusing the same source evaporator.

Encapsulation

Most OLED devices are sensitive to moisture and/or oxygen so they arecommonly sealed in an inert atmosphere such as nitrogen or argon, alongwith a desiccant such as alumina, bauxite, calcium sulfate, clays,silica gel, zeolites, alkaline metal oxides, alkaline earth metaloxides, sulfates, or metal halides and perchlorates. Methods forencapsulation and desiccation include, but are not limited to, thosedescribed in U.S. Pat. No. 6,226,890.

OLED Device Design Criteria

For full color display, the pixelation of LELs can be needed. Thispixelated deposition of LELs is achieved using shadow masks, integralshadow masks, U.S. Pat. No. 5,294,870, spatially defined thermal dyetransfer from a donor sheet, U.S. Pat. Nos. 5,688,551, 5,851,709, and6,066,357, and inkjet method, U.S. Pat. No. 6,066,357.

OLED devices of this invention can employ various well-known opticaleffects in order to enhance its properties if desired. This includesoptimizing layer thicknesses to yield maximum light transmission,providing dielectric mirror structures, providing reflective layers ormicrocavity structures, replacing reflective electrodes withlight-absorbing electrodes, providing anti-glare or anti-reflectioncoatings over the display, providing a polarizing medium over thedisplay, or providing colored, neutral density, or color-conversionfilters over the display. Filters, polarizers, and anti-glare oranti-reflection coatings may be specifically provided over the cover oras part of the cover.

Embodiments of the invention may provide EL devices that have goodluminance efficiency and good operational stability. Embodiments of theinvention may also give reduced voltage rises over the lifetime of thedevices and can be produced with high reproducibility and consistentlyto provide good light efficiency. They may have lower power consumptionrequirements and, when used with a battery, provide longer batterylifetimes.

EXPERIMENTAL EXAMPLES Examples 1 and 2 Preparation of InventiveCompounds A-2 and A-1

To an 100 mL dry, three-necked round flask were charged 4-5bromo-4′-(9-carbazolyl)biphenyl (2.0 g, 5 mmol) (Ref. Chem. Mater. 1998,10, 2235), 9(10H)-acridone (1.0 g, 5 mmol), K₂CO₃ (1.0 g, 7.5 mmol),copper (0.33 g, 5 mmol), CuI (0.1 g),2,2,6,6-tetramethyl-3,5-heptanedione (0.2 g), and MS-dried DMF (30 mL).The mixture was degassed and refluxed under nitrogen atmosphere for 24 h(The reaction may have completed in less than 24 h). After cooling toroom temperature, the precipitates from the reaction mixture werecollected by filtration, washed with 3 N HCl, water and methanol, anddried in air. The light yellow solid was dissolved in CH₂Cl₂ (smallamount of copper was left as brown particles) and purified by columnchromatography on silica gel with CH₂Cl₂-EtOAc (40:1 v/v) as elutingsolvents. The major fraction was collected and evaporation of thesolvents afforded 2.1 g of pure product A-2, yield 82%. The material wasfurther purified by sublimation at 270-280° C. The same procedure wasused to prepare A-1.

Example 3 Preparation of Devices 3.1 through 3.4.

A series of EL devices (3.1 through 3.4) were constructed in thefollowing manner:

-   1. A glass substrate coated with an 85 nm layer of indium-tin oxide    (ITO), as the anode, was sequentially ultrasonicated in a commercial    detergent, rinsed in deionized water, and exposed to oxygen plasma    for about 1 min.-   2. Over the ITO was deposited a 1 nm fluorocarbon (CFx)    hole-injecting layer (HIL) by plasma-assisted deposition of CHF₃ as    described in U.S. Pat. No. 6,208,075.-   3. Next a layer of hole-transporting material    4,4′-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) was deposited    to a thickness of 75 nm (HTL).-   4. Next an exciton block layer (EBL) of 10 nm of    4-(9H-carbazol-9-yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]-benzenamine    was deposited.-   5. A 20 nm light-emitting layer (LEL) composed of host material as    listed in Table 1 and 6% phosphorescent dopant Ir(ppy)₃ was then    deposited.-   6. A 50 nm electron-transporting layer (ETL) of Bphen was    vacuum-deposited over the LEL.-   7. A 0.5 electron-injection layer (EIL) of LiF was vacuum deposited    over the ETL-   8. And finally, a 100 nm layer of aluminum was deposited onto the    EIL, to form the cathode.

The above sequence completes the deposition of the EL devices. Thedevices were then hermetically packaged in a dry glove box forprotection against ambient environment. The devices thus formed weretested for luminous efficiency at an operating current of 1 mA/cm² andthe results are reported in Table 1. % EQE is the external quantumefficiency.

TABLE 1 Experimental Results Comp-1

Comp-2

Drive Example Volt. Efficiency (Type) LEL % EQE (Volts) (cd/A) 3.1Comp-1 13.4 3.99 47.0 (Comparative) 3.2 Comp-2 13.4 7.82 46.5(Comparative) 3.3 A-1 14.0 2.79 49.1 (Inventive) 3.4 A-2 16.9 3.29 58.9(Inventive)

Table 1 shows experimental results for a LEL using a phosphorescentlight-emitting compound. Comparison host materials Comp-1 (abis-acridone) and Comp-2 (a bis-carbazole) are symmetrical compounds.The inventive compounds A-1 and A-2, both of which bear one acridone andone diphenylamine or carbazole group, clearly offer improved performancein terms of efficiency and drive voltage.

Example 4 Preparation of Devices 4.1 through 4.3.

A series of EL devices (4.1 through 4.3) were constructed in the samemanner as Devices 3.1-3.4 except that the light-emitting phosphorescentmaterial in step 5 was replaced by 1% FD-54, a light-emittingfluorescent material, and the thickness of the ETL in step 6 wasdecreased to 40 nm.

The devices thus formed were tested for luminous efficiency at anoperating current of 1 mA/cm² and the results are reported in Table 2.

TABLE 2 Experimental Results Drive Example Volt. Efficiency (Type) LEL %EQE (Volts) (cd/A) 4.1 Comp-1 2.1 3.87 2.58 (Comparative) 4.2 A-1 4.12.91 5.67 (Inventive 4.3 A-2 5.3 3.43 5.55 (Inventive)

Table 1 shows experimental results for a LEL using a fluorescentlight-emitting compound. The inventive compounds A-1 and A-2, both ofwhich bear one acridone and one diphenylamine or carbazole group,clearly offer improved performance in terms of efficiency and drivevoltage relative to Comp-1, which lacks the diarylamino or carbazolegroup of the acridones of the invention.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. The patents and other publications referred to areincorporated herein in their entirety.

PARTS LIST 100 OLED 110 Substrate 120 Anode 130 Hole-Injecting layer(HIL) 132 Hole-Transporting layer (HTL) 134 Light-Emitting layer (LEL)135 Hole-Blocking Layer (HBL) 136 Electron-Transporting layer (ETL) 138Electron-Injecting layer (EIL) 140 Cathode 150 Voltage/Current Source160 Electrical Connectors

1. An OLED device comprising a cathode, an anode, and havingtherebetween a layer containing an acridone compound wherein theacridone compound is according to the following formula:

wherein: R₁ and R₂ are substituents; x and y are independently 0 to 4; Lis a linking group consisting of an unbroken chain of 6 to 36 aromatic,olefinic or acetylenic carbon atoms; and Ar₁ and Ar₂ are independentlyaromatic groups of 6 to 30 carbon atoms or are connected together toform a carbazole group.
 2. The OLED device of claim 1 wherein the layercontaining the acridone compound is a light-emitting layer including alight-emitting dopant.
 3. The OLED device of claim 2 wherein thelight-emitting dopant is fluorescent.
 4. The OLED device of claim 3wherein the fluorescent light-emitting dopant is a bis(azinyl)amineboron compound.
 5. The OLED device of claim 2 wherein the light-emittingdopant is phosphorescent.
 6. The OLED device of claim 5 wherein thephosphorescent dopant is an iridium complex.
 7. The OLED device of claim1 including a light-emitting layer and where the layer containing theacridone compound is a hole-blocking layer located between thelight-emitting layer and the cathode.
 8. The OLED device of claim 1wherein x and y are both 0 and L is phenyl or biphenyl.
 9. The OLEDdevice of claim 8 wherein Ar₁ and Ar₂ are phenyl groups.
 10. The OLEDdevice of claim 8 wherein Ar₁ and Ar₂ are joined together to form acarbazole group.
 11. A method of emitting light comprising applying anelectric potential across the device of claim
 1. 12. A displaycomprising the device of claim 1.